1. Field of the Invention
The present invention relates generally to well casing hangers in petroleum production wells. More specifically, the present invention relates to a full bore wellhead having a retractable load shoulder for suspending a casing.
2. Description of the Related Art
In some types of wellhead assemblies casing is suspended by a casing hanger on a load shoulder formed in the bore of the wellhead housing. Generally the load shoulder is formed integrally or permanently attached to the wellhead housing. The fixed load shoulder results in a reduced diameter in the bore below the load shoulder. Any tools or pipe must be smaller than the fixed shoulder. In some wells, more than one load shoulder is utilized for supporting multiple strings of casing.
Retrievable load shoulders are also known in the art, employing a running tool to deploy and retrieve the load shoulder selectively. Also, the prior art includes retractable load shoulders that are installed with the wellhead housing, but retracted before running casing. Retrievable and retractable load shoulders provide full bore access.
A wellhead load ring constructed in the shape of a C-ring is pre-installed in a wellhead in a storage position that maintains full bore of the wellhead. The load ring is preferably secured in this position by shear pins. The shear pins are sheared by a tool that pushes the load ring into an operational position, where it rests on a landing shoulder of a support ring. The load ring is further secured in this position by one of several latching methods.